It has been long recognized that present day screw drivers fall far short of being adequate to insert or remove screws which have substantial resistance to turning. Most typically, if a screw has a substantial resistance to being turned, upon applying a torque thereto, the screw driver blade slips upwardly out of the slot in the screw head. This slippage is an undesirable result arising from the current screw driver blade geometry.
Many attempts have been made to modify screw driver blades to make them perform better when in use on "difficult-to-turn" screws. Representative of these attempts are U.S. Pat. Nos. 3,236,275; 2,684,094 and 370,255. Generally, these attempts have included modifying the screw head as well as the screw driver blade. However, modification of the screw head is impractical, since screws currently in use do not have modified heads and industry acceptance of any modification is a major obstacle. Another approach is to modify the screw driver blade by providing ribs which project downwardly on each side of the screw head as shown in U.S. Pat. No. 697,836. However, such a screw driver is generally unacceptable since the screw head must be protruding above any adjacent surfaces in order for the screw driver to be used.
Also, it has become important from a quality control point of view to avoid burring the upper edges of the screw slot during its insertion into its final use position. None of the prior art screw drivers suggest a means of avoiding such burring.
The invention of this application is a rugged, inexpensive, readily constructed and easily employed screw driver which overcomes all of the defects of prior art screw drivers.